Node judging method, communication system, and node measuring apparatus

ABSTRACT

In a communication system wherein a station transceiver and a plurality of nodes communicate in a TDM system through a signal transmission line, at least apart of the line is shared, a method to judge nodes performing normal operation from the station transceiver comprises a request step to request a return of a test pattern by transmitting a trigger signal for a designated node in the plurality of nodes, a correlation process step to process correlation between a received signal in a timeslot assigned to the designated node and a reference pattern corresponding to the designated node, and a judging step to judge whether the designated node is a normal node according to the correlation process result.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application is based upon the benefit of priority from theprior Japanese Patent Application No. 2001-357010, filed on Nov. 22,2001, the entire contents of which are incorporated herein by reference.

FIELD OF THE INVENTION

[0002] This invention relates to a node judging method, a communicationsystem, and a node measuring apparatus, and more specifically relates toa method for detecting a disturbing node and its communication system,and a node measuring apparatus for detecting the disturbing node.

BACKGROUND OF THE INVENTION

[0003]FIG. 7 shows a schematic diagram of a passive optical subscribernetwork of TDM (time division multiplexing) system, which connects asingle station transceiver and a plurality of subscriber nodes.

[0004] A station transceiver 110 connects to a common port #C of opticalmultiplexer/demultiplexer 114 through an optical fiber 112. The opticalmultiplexer/demultiplexer 114 comprises an optical element todemultiplex an input light from the common port #C into N portions andoutput each demultiplexed light through ports #1˜#N, and to multiplexinput light from each of the ports #1˜#N and output the multiplexedlight through the common port #C. Each of the ports #1˜#N of the opticalmultiplexer/demultiplexer 114 connects to each of optical transceivers118-1˜118-N belonging to respective subscribers #1˜#N via optical fibers116-1˜116-N.

[0005] A TDM system is used for the communication between the stationtransceiver 110 and each of the optical transceivers 118-1˜118-Nbelonging to the subscribers #1˜#N respectively. Namely, each of theoptical transceivers 118-1˜118-N extracts a signal in a timeslotassigned for itself out of the time division multiplexed signals (downsignal) from the station transceiver 110, receives the extracted signal,and discards the rest of the signal lights in the other timeslots. Eachof the optical transceivers 118-1˜118-N also outputs a signal to betransmitted for the station transceiver 110 onto the respective opticalfibers 116-1˜116-N at timing according to its own assigned timeslot. Thestation transceiver 110 predeterminedly and continuously synchronizesthe station transceiver 110 and the optical transceivers 118-1˜118-N. Bythis operation, each of the optical transceivers 118-1˜118-N is able toknow the timing of its assigned timeslot for transmission and reception.Description for the synchronizing procedure between the stationtransceiver 110 and the optical transceivers 118-1˜118-N is omittedhere.

[0006] Used as a down signal to transmit from the station transceiver110 to the optical transceivers 118-1˜118-N belonging to the respectivesubscribers #1˜#N and an up signal from the optical transceivers118-1˜118-N belonging to the respective subscribers #1˜#N to the stationtransceiver 110 are optical carriers having a wavelength different fromeach other. In a conventional system, a 1.5 μm band optical carrier isused for the down signal and a 1.3 μm band optical carrier is used forthe up signal.

[0007] The operation of a conventional system is explained below. Thestation transceiver 110 time-division-multiplexes a down optical signalDi (i=1−N) destined for the respective subscribers #1˜#N and outputsonto the optical fiber 112. The down optical signal Di propagates on theoptical fiber 112 and enters a common port #C of the opticalmultiplexer/demultiplexer 114. The optical multiplexer/demultiplexer 114divides the time-division-multiplexed down optical signal Di into Nportions and outputs each divided light onto the optical fibers116-1˜116-N through the ports #1˜#N. Formatively, all the down opticalsignals D1˜DN destined for the respective subscribers #1˜#N enter everyone of the transceivers 118-1˜118-N. Each of the optical transceivers118-1˜118-N extracts an optical signal in a timeslot assigned for itselfout of the input optical signals, receives the extracted signal, anddiscards the rest of the optical signals in the other timeslots. Forinstance, the optical transceiver 118-1 exclusively receives a downoptical signal D1, and the optical transceiver 118-2 exclusivelyreceives a down optical signal D2.

[0008] Each of the optical transceivers 118-1˜118-N outputs an upoptical signal Ui (i=1˜N) according to its own assigned timeslot ontothe optical fibers 116-1˜116-N. The up optical signal Ui (i=1˜N)propagates on the optical fibers 116-1˜116-N and enters the ports #1˜#Nof the optical multiplexer/demultiplexer 114 respectively. The opticalmultiplexer/demultiplexer 114 multiplexes the respective up opticalsignals Ui (i=1˜N) from the optical fibers 116-1˜116-N) and outputs ontothe optical fiber 112 through the common port #C.

[0009] When the optical transceivers 118-1˜118-N output the opticalsignal Ui (i=1˜N) onto the optical fibers 116-1˜116-N in the respectiveassigned appropriate timeslots, the up optical signals Ui on the opticalfiber 112 are located on proper timeslots not overlapping each other inthe time domain, as shown in FIG. 7. That is, the opticalmultiplexer/demultiplexer 114 multiplexes the respective up opticalsignals Ui without adjusting their time locations.

[0010] The up optical signal Ui being output onto the optical fibers 112from the optical multiplexer/demultiplexer 114 transmits on the opticalfiber 112 and enters the station transceiver 110. Since the stationtransceiver 110 synchronizes with each of the optical transceivers118-1˜118-N, it can accurately separate each up optical signal Ui out ofthe input optical signals from the optical fiber 112.

[0011] In the above-described passive optical subscriber network, aplurality of subscribers shares one signal band in the time domain.Therefore, when one of the subscribers' units outputs an up opticalsignal in a timeslot other than the one assigned to itself due to somefault, the other subscriber's communication originally using themistaken timeslot is inhibited.

[0012] For instance, supposing that the optical transceiver 118-1outputs a continuous disturbance light onto the optical fiber 116-1,this disturbance light extremely deteriorates a signal-to-noise powerratio (SNR) of the up optical signals U2˜UN, which are output for thestation transceiver 110 by the other optical transceivers 118-2˜118-N,on the optical fiber 112. This inhibits signal transmission from theoptical transceivers 118-2˜118-N to the station transceiver 110. Thiskind of situation can be occurred when a subscriber is confused ofconnecting optical fiber codes and connects to a wrong communicationdevice by mistake or a subscriber maliciously outputs an up opticalsignal that is not permitted.

[0013] When this type of fault occurs, it is most important to eliminatethe fault factor as soon as possible. In particular, when thedisturbance optical signal is transmitted continuously, all thesubscribers' signals are interrupted and thus it is necessary to solvethe problem without a moment's delay. However, conventionally, toidentify the one outputting the disturbance light out of all the opticaltransceivers 1181˜118-N was impossible and thus there was no other waybut to check every transceiver one by one.

SUMMARY OF THE INVENTION

[0014] A node judging method according to the present invention is amethod to judge nodes of normal performance from a station transceiverside in a communication system wherein the station transceiver and aplurality of nodes communicate in a TDM system through a signaltransmission line in which at least a part of the line is shared andcomprises a request step to request a return of a test pattern bytransmitting a trigger signal for a designated node in the plurality ofnodes, a correlation process step to process correlation between areceived signal in a timeslot assigned to the designated node and areference pattern corresponding to the designated node, and a judgingstep to judge whether the designated node is a disturbance nodeaccording to the correlation process result.

[0015] A communication system according to the present invention is asystem wherein a station transceiver and a plurality of nodescommunicate in a TDM system through a signal transmission line in whichat least a part of the line is shared, and is characterized in that thestation transceiver comprises a trigger signal transmitter to transmit atrigger signal including a synchronous pattern signal for the designatednode, a reference pattern generator to generate a reference patterncorresponding to the designated node, a correlation processor to processcorrelation between a received signal in a timeslot assigned to thedesignated node and the reference pattern, and a judging apparatus tojudge whether the designated node is a normal node according to acorrelation processed result by the correlation processor and each ofthe plurality of nodes comprises an apparatus to output a predeterminedtest pattern signal according to the trigger signal.

[0016] A node measuring apparatus according to the present inventioncomprises a trigger transmitter to transmit a trigger signal for adesignated node in the plurality of nodes to request the designated nodeto return a test pattern signal, a reference patter generator togenerate a reference pattern corresponding to the designated node,correlation processor to process correlation between a received signalin a timeslot assigned to the designated node and the reference pattern,and a judging apparatus to judge whether the designated node is a normalnode according to the correlation process result from the correlationprocessor.

BRIEF DESCRIPTION OF THE DRAWING

[0017] The above and other objects, features and advantages of thepresent invention will be apparent from the following detaileddescription of the preferred embodiments of the invention in conjunctionwith the accompanying drawings, in which:

[0018]FIG. 1 is a schematic block diagram of an embodiment according tothe present invention;

[0019]FIG. 2 is a schematic block diagram of a station transceiver 10;

[0020]FIG. 3 shows waveform examples of correlation result andintegration result when a received test pattern and a reference patterncoincide;

[0021]FIG. 4 shows waveform examples of correlation result andintegration result when a received test pattern and a reference patterndo not coincide;

[0022]FIG. 5 is a schematic block diagram of another configurationexample of the station transceiver 10;

[0023]FIG. 6 is a schematic block diagram of an optical transmitter18-1; and

[0024]FIG. 7 is a schematic block diagram of a passive opticalsubscriber network of a conventional TDM (time division multiplexing)system.

DETAILED DESCRIPTION

[0025] Embodiments of the invention are explained below in detail withreference to the drawings.

[0026]FIG. 1 is a schematic block diagram of an embodiment of thepresent invention.

[0027] A station transceiver 10 connects to a common port #C of anoptical multiplexer/demultiplexer 14 through an optical fiber 12. Theoptical multiplexer/demultiplexer 14 comprises an optical element todivide an input light through the common port #C into N portions andoutput each divided light for ports #1˜#N, and to multiplex input lightsfrom the ports #1˜#N and output through the common port #C. The ports#1˜#N of the optical multiplexer/demultiplexer 14 connect to opticaltransceivers 18-1˜18-N belonging to respective subscribers #1˜#N throughoptical fibers 16-1˜16-N respectively.

[0028] Communication between the station transceiver 10 and the opticaltransceivers 18-1˜18-N of the subscribers #1˜#N is identical to that ofthe conventional system shown in FIG. 7. That is, a TDM system is usedin communication between a station transceiver 10 and the opticaltransceivers 18-1˜18-N belonging to the subscribers #1˜#N, and an upsignal and a down signal is distinguished by a wavelength of an opticalcarrier to be used. In this embodiment, an optical carrier of wavelengthλd is used for the down signal from the station transceiver 10 to theoptical transceivers 18-1˜18-N belonging to the respective subscribers#1˜#N, and an optical carrier of wavelength λu different to thewavelength λd is used for the up signal from the optical transceivers18-1˜18-N of the respective subscribers #1˜#N to the station transceiver10. Similarly to the conventional system, λd is 1.5 Am band and λu is1.3 μm.

[0029] In FIG. 1, the transceiver 18-2 plays a role of a disturbancenode to regularly output disturbance lights onto the optical fiber 16-2.The operation of this embodiment to identify the disturbance node (theoptical transceiver 18-2) is explained below in detail.

[0030] The station transceiver 10 comprises a node measuring apparatusto measure disturbance nodes and fault occurrences. In the explanationbelow, the operation of the station transceiver 10 to measure whether anode is normal or not is the operation of the node measuring apparatusbuilt in the station transceiver 10.

[0031] First, the station transceiver 10 instructs all the opticaltransceivers 18-1˜18-N to be tested or one or some of the test objectsto shift to a test mode.

[0032] The station transceiver 10 periodically outputs an opticaltrigger signal 20 (wavelength λd) for the optical fiber 12 so that therespective optical transceivers 18-1˜18-N transmit a test patternaccording to the predetermined timing. The optical trigger signal 20comprises a node designator 20 a that designates an optical transceiverto return a test pattern and an idle pattern signal 20 b to synchronizethe object optical transceiver with the station transceiver 10. The nodedesignator 20 a can designate a single specific one in the opticaltransceivers 18-1˜18-N and also can specify all the optical transceivers18-1˜18-N at once. In FIG. 1, the node designator 20 a designates theoptical transceiver 18-1. The idle pattern signal 20 b can be identicalto the test pattern to be returned from the optical transceivers18-1˜18-N and also can be a fixed pattern made from a constantrepetition of mark and space.

[0033] An optical multiplexer/demultiplexer 14 divides the opticaltrigger signal 20 input from the station transceiver 10 through theoptical fiber 12 into N portions and outputs the respective dividedlight for the optical transceivers 18-1˜18-N through the optical fibers16-1˜16-N. Only the optical transceiver 18-1 designated by the nodedesignator 20 a in the optical trigger signal 20 outputs a test patternoptical signal 22 onto the optical fiber 16-1. At this time, the opticaltransceiver 18-1 synchronizes with an idle pattern signal 20 b in theinput optical trigger signal 20 and outputs an optical test patternsignal 22 (wavelength λu) for the optical fiber 16-1. Through thisoperation, the synchronization between the station transceiver 10 andthe optical transceiver 18-1 is confirmed.

[0034] The test pattern carried by the test pattern optical signal 22(wavelength λu) can be any pattern as far as the station transceiver 10recognizes it. For instance, it can be identical to the idle pattern 20b or an encoded idle pattern and also can be identical or different inthe respective optical transceivers 18-1˜18-N. However, it is preferablethat the test pattern comprises a pseudo random pattern.

[0035] When all the optical transceivers 18-1˜18-N are tested at thesame time, it is preferable that the optical transceivers 18-1˜18-Nreturn a test pattern optical signal comprising a pattern different fromeach other to the station transceiver 10. Because, when some of theoptical transceivers locate on the same distance from the stationtransceiver 10, the station transceiver 10 cannot detect the testpattern optical signals from those transceivers individually even if ituses a correlation method to be described later.

[0036] When a single optical transceiver is tested one by one, each ofthe optical transceivers 18-1˜18-N can either returns the same testpattern optical signal 22 to the station transceiver 10 or returns atest pattern optical signal 22 different from each other to the stationtransceiver 10.

[0037] The test pattern optical signal 22 being output from the opticaltransceiver 18-1 propagates on the optical fiber 16-1 and enters theoptical multiplexer/demultiplexer 14. Also, the disturbance light 24(wavelength λu) being output from the optical transceiver 18-2 onto theoptical fiber 16-2 propagates on the optical fiber 16-2 and enters theoptical multiplexer/demultiplexer 14. The opticalmultiplexer/demultiplexer 14 applies its test pattern optical signal 22(wavelength λu) and the disturbance light 24 (wavelength λu) to thestation transceiver 10 through the optical fiber 12. On the opticalfiber 12, an SNR of the test pattern optical 22 greatly deteriorates dueto the disturbance light 24.

[0038] The station transceiver 10 converts the light consisted of thetest pattern optical signal 22 and the disturbance light 24 input fromthe optical fiber 12 to an electric signal, processes the correlationbetween the output and the reference pattern, and integrates thecorrelation result. The reference pattern comprises a pattern identicalto the test pattern carried by the test pattern optical signal 22. Fromthis correlation process, the test pattern optical signal 22 can bedetected. Even when the SNR of the test pattern optical signal 22 isgreatly deteriorated, the test pattern optical signal 22 can becertainly detected by integrating the correlation result.

[0039] Although the details are described later, when the test patternis detected, the reference pattern is applied to a correlation processcircuit after the trigger optical signal 20 is output onto the opticalfiber 12, the time lag equals to the time needed for the roundtripdistance between the optical transceiver to be tested (here, theapparatus 18-1) and the station transceiver 10 plus the return time inthe apparatus 18-1. By applying the reference pattern to the correlationprocess circuit at the timing where the test pattern does not exist, across-correlation value with the signal input from the optical fiber 12can be calculated. This cross-correlation value shows an index ofbackground noise.

[0040] If the integration value of the correlation result is larger thanthe predetermined value, it proves that the subject optical transceiverbeing tested is normally operated. The station transceiver 10 outputsthe trigger optical signal 20 on to the optical fiber 12 taking a nextoptical transceiver, for instance the apparatus 18-2, as a testingobject. According to this manner, the station transceiver 10 tests eachof the optical transceivers 18-1˜18-N one by one.

[0041] The optical transceiver 18-2 outputting the disturbance light 24does not send a test pattern optical signal in return to the triggeroptical signal 20. Therefore, when the optical transceiver 18-2 has beentested, the integration value of correlation process in the stationtransceiver 10 is lower than the predetermined value. From this, it isclear that the station transceiver 10 recognizes a fault in the opticaltransceiver 18-2.

[0042] When each of the optical transceivers 18-1˜18-N outputs a testpattern optical signal different from each other, the stationtransceiver 10 can identify an optical transceiver having a fault, e.g.fault node, quicker by performing correlation process in parallel.Needless to say, the station transceiver 10 can perform correlationprocess of the test pattern optical signal from each of the opticaltransceivers 18-1˜18-N sequentially. This requires less time to identifythe fault node compared to the method that outputs the trigger opticalsignal 20 for the optical transceivers 18-1˜18-N individually.

[0043] Generally, when a disturbance light exists, it is expected thatall the up signals are being disturbed. However, sometimes it happensthat a disturbance light is transmitted in a timeslot other than thepredetermined timeslot due to a defect of timing circuits etc. In thiscase, the transmission timing is likely to have periodicity, and thusalthough it affects one or some of other subscribers, it does not affectthe communication of the rest of the subscribers. Under thecircumstance, to avoid the influence to the nodes performing normalcommunication, the above detecting process is performed in the situationthat only the node having communication fault is enforced to send testpattern data instead of communication data for a station to which thenode having fault has been assigned. In this case, it is necessary toperform integral process only when the test pattern data exists.

[0044] The internal configuration of the station transceiver 10 isexplained below. FIG. 2 shows a schematic block diagram of an embodimentof the station transceiver 10. However, it mainly shows a configurationof a node measuring apparatus to measure whether the transceivers18-1˜18-N operate normally. A control circuit 30 applies a subscriber IDto identify an optical transceiver to be tested and idle pattern to anoptical transmitter 32 and applies a trigger signal and delay timeobtained by considering roundtrip distance between the opticaltransceiver to be tested and the station transceiver 10 to a referencepattern generating circuit 34.

[0045] The optical transmitter 32 converts the subscriber ID and idlepattern signal into an optical signal of wavelength λd to generate atrigger optical signal 20 whose retrieval object is identified by thesubscriber ID. The trigger optical signal 20 is applied to the opticalfiber 12 through a WDM optical multiplexer/demultiplexer 36 and sent forthe optical transceivers 18-1˜18-N as previously explained.

[0046] The WDM optical multiplexer/demultiplexer 36 is awavelength-selective optical coupler to couple the λd light output fromthe optical transmitter 32 to the optical fiber 12 and input the lightof wavelength λu from the optical fiber 12 to an optical receiver 58.

[0047] The WDM optical multiplexer/demultiplexer 36 applies the light ofwavelength λu including the test pattern optical signal 22 anddisturbance light 24 from the optical fiber 12 into the optical receiver38. The optical receiver 38 converts the input light into an electricsignal and applies to a correlation processor 40. A test pattern carriedby the test pattern optical signal 22 enters the correlation processor40.

[0048] On the other hand, the reference pattern generator 34 generates areference pattern when the delay time set by the controller 30 passedfrom inputting the trigger signal from the controller 30 and applies thereference pattern to the correlation processor 40. The reference patterngenerator 34 also applies a gate signal to the integrator 42, the gatesignal showing a timeslot used by the optical transceiver to output atest pattern optical signal for the correlation result from thecorrelation processor 40. The gate signal shows the timing to integratethe correlation process result for the test pattern signal from thetested optical transceiver.

[0049] The correlation processor 40 processes the correlation betweenthe received test pattern from the optical receiver 38 and the referencepattern from the reference pattern generator 34 and applies thecorrelation result to the integrator 42. The integrator 42 integratesthe correlation result from the correlation processor 40 in a timeslotassigned by the gate signal from the reference pattern generator 34.

[0050] The controller 30 specifies one or more optical transceiversgenerating the disturbance light according to the integration result foreach of the optical transceivers 18-1˜18-N by the integrator 42.

[0051]FIG. 3 shows waveforms of correlation result and integrationresult when a received test pattern and a reference pattern coincide,and FIG. 4 shows waveforms of correlation result and integrated resultwhen the received test pattern and the reference pattern do notcoincide. When the received test pattern and the reference patterncoincide, the integration result of the integrator 42 increases withtime. This means that the tested optical transceiver is operatingnormally and not outputting the disturbance light. Conversely, when thereceived test pattern and the reference pattern do not coincide, theintegration result of the integrator 42 only varies around zero value orwithin minus values. This means that the tested optical transceiver isnot operating normally and outputting the disturbance light. Asdescribed above, it is possible to judge whether the tested opticaltransceiver is operating normally or not, namely outputting disturbancelight or not, according to the integration result output from theintegrator 42.

[0052] When the reference pattern generator 34, correlation processor40, and integrator 42 are designed as a digital processor, ananalog/digital (A/D) converter should be disposed between the opticalreceiver 38 and the correlation processor 40.

[0053] As explained above, the disturbance node can be specified morequickly owing to the configuration in which the test pattern opticalsignals are output in the timeslots assigned respectively by theplurality of optical transceivers 18-1˜18-N, and the station transceiver10 performs correlation process of the plurality of received testpattern signals spontaneously.

[0054]FIG. 5 shows a schematic block diagram of an embodiment of thestation transceiver 10 to perform parallel processing of a plurality ofreceived test pattern signals.

[0055] A trigger generator 50 applies an identifier to show all or someof the optical transceivers 18-1˜18-N and an idle pattern to an opticaltransmitter 52. The optical transmitter 52 generates a trigger opticalsignal 20 (wavelength λd) to be broadcasted or multicasted to all orsome of the optical transceivers 18-1˜18-N, and, at the same time,applies a trigger signal to show test-start timing to the correlationjudging circuits 54-1˜54-N to judge correlation of the test patternsreturned from each of the optical transceivers 18-1˜18-N. Delay time isapplied to each of the correlation judging circuits 54-1˜54-N, eachdelay time is determined considering roundtrip distance from the stationtransceiver 10 to the corresponding optical transceivers 18-1˜18-N. Thetrigger optical signal 20 (wavelength λd) generated by the opticaltransmitter 52 is applied to the optical fiber 12 through the WDMoptical multiplexer/demultiplexer 56 and, as previously explained,enters the optical transceivers 18-1˜18-N. The WDM opticalmultiplexer/demultiplexer 56 comprises an optical element identical tothe WDM multiplexer/demultiplexer 36.

[0056] The WDM optical multiplexer/demultiplexer 56 applies the light ofwavelength λu from the optical fiber 12 to the optical receiver 58. Theoptical receiver 58 converts the light of wavelength λu from the WDMoptical multiplexer/demultiplexer 56 into an electric signal and appliesto each of the correlation judging circuits 54-1˜54-N. The output fromthe optical receiver 58 includes the test pattern signal returned fromthe optical transceiver assigned by the trigger optical signal 20 andthe disturbance light from the disturbance node.

[0057] Each of the correlation judging circuits 54-1˜54-N comprises aconfiguration identical to the circuit block diagram of the embodimentshown in FIG. 1, which consists of the reference pattern generator 34,the correlation processor 40 and the integrator 42. Performing the sameoperation to the one explained for the embodiment in FIG. 1, eachcorrelation judging circuit 54-1˜54-N judges according to the outputfrom the optical receiver 58 whether the corresponding opticaltransceiver 18-1˜18-N normally returns a test pattern signal. Judgedresult of each correlation judging circuit 54-1˜54-N corresponds to theoutput from the integrator 42. The judged result of each correlationjudging circuit 54-1˜54-N is applied to a judging circuit 60. Thejudging circuit 60 specifies which optical transceiver 18-1˜18-N outputsthe disturbance signal or light according to the judged output from eachcorrelation judging circuit 54-1˜54-N.

[0058] In the embodiment shown in FIG. 5, since it is possible toprocess in parallel the test pattern signals returned from the pluralityof optical transceivers 18-1˜18-N, the disturbance node can be detectedquickly.

[0059] In the embodiment shown in FIG. 5, it is also possible to convertthe analog output from the optical receiver 38 to a digital signal andapplies to each correlation judging circuit 54-1˜54-N.

[0060] There are two kinds of methods for generating a test patternsignal in each optical transceiver 18-1˜18-N. The first method is toreturn the pattern from the station transceiver 10 as it is or aftercoding it. In this method, the internal configuration of the opticaltransceiver 18-1˜18-N can be simplified. The second method is to use theidle pattern 20 b from the station transceiver 10 only for synchronizingwith the station transceiver 10 and each optical transceiver 18-1˜18-Ngenerates an original test pattern. In this case, each opticaltransceiver 18-1˜18-N requires a pattern generator, and the generatedpattern must be identical to the reference pattern generated in thestation transceiver 10.

[0061]FIG. 6 shows a schematic block diagram of an embodiment of theoptical transceiver 18-1 capable of generating an original test pattern.The other optical transceivers 18-2˜18-N also have the sameconfiguration.

[0062] A WDM optical multiplexer/demultiplexer 70 applies the lightinput from the optical fiber 16-1 to an optical receiver 72. The opticalreceiver 72 converts the timeslot part assigned to the opticaltransceiver 18-1 in the input light into an electric signal and outputsfor a transmission/reception circuit 74.

[0063] The transmission/reception circuit 74 transmits/receives datato/from the station transceiver 10 in communication mode. In test mode,the transmission/reception circuit 74 identifies ID showing return testpattern from the signal carried by the optical trigger signal from thestation transceiver 10 and applies to the test pattern generator 78, andapplies a synchronous signal for synchronizing the test pattern with theidle pattern to the test pattern generator 78. The test patterngenerator 78 generates a test pattern having a pattern-content accordingto the ID identified by the ID identifier 76 in synchronization with thesynchronous signal from the transmission/reception circuit 74 andapplies to a b-contact of switch 80.

[0064] The transmission/reception circuit 74 also receives controlcommand for the optical transceiver 18-1 and controls each part of theoptical transceiver 18-1 according to the received command. Forinstance, although a switch 80 normally connects to a-contact (theoutput of the transmission/reception circuit 74), thetransmission/reception circuit 74 connects the switch 80 to theb-contact (the output of the test pattern generator 78) when it receivesa command to instruct shifting to the test mode from the stationtransceiver 10.

[0065] The signal selected at the switch 80 is applied to the opticaltransmitter 82 and converted to an optical signal of wavelength λu. Theoptical signal (wavelength λu) output from the optical transmitter 82 istransmitted onto the optical fiber 16-1 by the WDM opticalmultiplexer/demultiplexer 70 and enters the station transceiver 10through the optical fiber 16-1, the optical multiplexer/demultiplexer14, and the optical fiber 12.

[0066] In the test mode, since the switch 80 connects to the b-contact,the test pattern optical signal 22 to carry the test pattern output fromthe test pattern generator 78 is transmitted from the opticaltransceiver 18-1 to the station transceiver 10.

[0067] Although explained above is an embodiment in which a nodemeasuring apparatus is built in the station transceiver 10, aconfiguration such that a node measuring apparatus with theabove-described function is disposed outside the station transceiver isobviously applicable.

[0068] As readily understandable from the aforementioned explanation,according to the invention, even if communication of a TDM opticalnetwork is inhibited due to a fault of a specific node apparatus, it ispossible to check normally operating nodes easily and precisely. Thatis, the node having the fault is identified quickly.

[0069] While the invention has been described with reference to thespecific embodiment, it will be apparent to those skilled in the artthat various changes and modifications can be made to the specificembodiment without departing from the spirit and scope of the inventionas defined in the claims.

1. In a communication system wherein a station transceiver and aplurality of nodes communicate in a TDM system through a signaltransmission line, at least apart of the line is shared, a method tojudge nodes performing normal operation from the station transceivercomprising: a request step to request a return of a test pattern bytransmitting a trigger signal for a designated node in the plurality ofnodes; a correlation process step to process correlation between areceived signal in a timeslot assigned to the designated node and areference pattern corresponding to the designated node; and a judgingstep to judge whether the designated node is a normal node according tothe correlation process result.
 2. The node judging method of claim 1wherein the correlation process step starts the correlation processbetween the received signal and the reference pattern after thetransmission of the trigger with a time lag corresponding to theroundtrip distance of the signal to the designated node.
 3. The nodejudging method of claim 1 wherein the judging step comprises an integralstep to integrate the correlation process result for a predeterminedtime and judges whether the designated node is a normal node accordingto the integration result.
 4. The node judging method of claim 1 whereinthe request step comprises a trigger transmission step to transmit thetrigger signal including a synchronous pattern signal for the designatednode and a return step in which the designated node returns a testpattern in synchronization with the trigger signal.
 5. The node judgingmethod of claim 4 wherein the return step is a step in which thedesignated node returns the test pattern signal in a timeslot assignedto the designated node.
 6. The node judging method of claim 1 furthercomprising a step to select the designated node sequentially from theplurality of nodes and perform the request step, the correlation processstep, and the judging step.
 7. The node judging method of claim 1wherein each of the plurality of nodes returns a test pattern differentfrom each other for the trigger signal.
 8. The node judging method ofclaim 1 wherein at least two of the nodes are specified and the requeststep, the correlation step, and the judging step are executed.
 9. Thenode judging method of claim 8 wherein the correlation process for theplurality of designated nodes between a respective reference pattern andthe received signal are executed in parallel.
 10. The node judgingmethod of claim 1 wherein the signal transmission line comprises: afirst signal line to input/output signals to/from the stationtransceiver and node measuring apparatus; a plurality of second signallines to input/output a signal to/from each of the plurality of nodes;and a multiplexer/demultiplexer to supply the signal from the firstsignal line to each of the plurality of second signal lines and tosupply the signals from the plurality of second signal line to the firstsignal line.
 11. The node judging method of claim 10 wherein both of thefirst signal line and the plurality of second signal lines comprise anoptical fiber.
 12. A communication system wherein a station transceiverand a plurality of nodes communicate in TDM system through a signaltransmission line, at least a part of the line is shared, thecommunication system characterized in that; the station transceivercomprises: a trigger transmitter to transmit a trigger signal includingsynchronous pattern signal for a designated node; a reference patterngenerator to generate a reference pattern corresponding to thedesignated node; a correlation processor to process correlation betweena received signal in a timeslot assigned to the designated node and thereference pattern; and a judging apparatus to judge whether thedesignated node is a normal node according to a correlation processresult by the correlation processor; and each of the plurality of nodescomprises an apparatus to output a predetermined test pattern signalaccording to the trigger signal.
 13. The communication system of claim12 wherein the reference pattern generator generates the referencepattern after the transmission of the trigger signal with a time lagcorresponding to roundtrip distance between the station transceiver andthe designated node.
 14. The communication system of claim 12 whereinthe judging apparatus comprises integrator to integrate the processresult from the correlation processor for a predetermined time and tojudges whether the designated node is a normal node according to theintegration result.
 15. The communication system of claim 12 wherein thedesignated node outputs the test pattern signal in a timeslot assignedto the designated node.
 16. The communication system of claim 12 whereinthe station transceiver comprises the reference pattern generator,correlation processor, and the judging apparatus for each of theplurality of nodes.
 17. The communication system of claim 12 whereineach of the plurality of nodes sends a test pattern different from eachother in return to the trigger signal.
 18. The communication system ofclaim 12 wherein the signal transmission line comprises: a first signalline to input/output a signal to/from the station transceiver; aplurality of second signal lines to input/output a signal to/from eachof the plurality of nodes; and a multiplexer/demultiplexer to supply asignal from the first signal line to each of the plurality of secondsignal lines and to supply signals from the plurality of second signallines to the first signal line.
 19. The communication system of claim 18wherein both of the first signal line and the plurality of second signallines comprise an optical fiber.
 20. A node measuring apparatuscomprising: a trigger signal transmitter to transmit a trigger signalfor a designated node in a plurality of nodes to request the designatednode to return a test pattern signal in return; a reference patterngenerator to generate a reference pattern corresponding to thedesignated node; a correlation processor to process correlation betweena received signal in a timeslot assigned to the designated node and thereference pattern; and a judging apparatus to judge whether thedesignated node is a normal node according to the correlation processresult from the correlation processor.
 21. The node measuring apparatusof claim 20 wherein the reference pattern generator generates thereference pattern after the transmission of the trigger signal with atime lag corresponding to the roundtrip distance to the designated node.22. The node measuring apparatus of claim 20 wherein the judgingapparatus comprises an integrator to integrate the process result fromthe correlation processor for a predetermined time and judges whetherthe designated node is a normal node according to the integrationresult.
 23. The node measuring apparatus of claim 20 wherein thedesignated node outputs the test pattern signal in a timeslot assignedto the designated node according to the trigger signal.
 24. The nodemeasuring apparatus of claim 20 comprising the reference patterngenerator, the correlation processor, and the judging apparatus for eachof the plurality of nodes.